Flat bed knitting machines of this type are generally known and are described for example in the book by Dieter Tollkuhn "Flachstrick-automaten", 1979, publisher Meisenbach KG, Bamberg. Therein, the comb sinkers serve for the so-called "couliering" of the yarn wherein the thread taken up by the needle is held back during the withdrawal movement of the needle on the coulier (stitch-forming) edge of the comb sinker in order to form the stitch (c.f. e.g. pages 46 and 47 of the book). The comb sinkers, which are necessary for the formation of the stitch, may, for example, be stamped elements which are clipped into the needle bed. The comb sinkers may also however, as a part of the needle bed itself, be constructed as a single unit with the latter. In order to obtain a perfect knitted fabric, it is thereby necessary to exert a certain tension on each old stitch so that the stitches cannot move upwardly into the stitch forming region and be captured yet again by the needles. Consequently, the flat knitting machines have a fabric or stitch take-off device with which the old, finished stitches are removed.
Nowadays, there is a demand for flat knitting machines with which the most varied patterns can be knitted, for example knots, cable stitches or fancy trimmed knitted sections, for incorporation in the knitwear or attachment to the knitted fabric. It is necessary with these patterns however, that several stitches be located on one needle or that new stitches be incorporated into the stitches without taking-off the fabric. This has the result that the additional new stitches are not captured by the fabric or stitch take-off mechanism and thus are not drawn off. Consequently, especially with patterns of this type, there is a great danger that these additional stitches, upon which no tension is being exerted, will move upwardly into the region of stitch formation or needle movement.
So-called stitch pressers, in which a presser wire or finger in the camming region in the comb gap is simultaneously moved in the direction of movement of the cam and holds down the stitches not captured by the fabric or stitch take-off mechanism, have already been used. Apart from the fact that differently shaped pressers are also required for the different kinds of knitting and the different gauges, which entails a frequent swapping-over of the pressers, it is also especially disadvantageous that the pressers likewise have to be switched over upon the return of the carriage. Moreover, the wires of the presser are easily bent out of shape, come into contact with the latch brushes and impede the access to and the view into the comb gap.
Flat bed knitting machines are known for example from the publications DE-A 39 17 934, DE-PS 233 559, CH-PS 343 573, DE-AS 15 85 281, DE-A 20 61 502 or DE- A 36 09 539, in which the comb sinkers are constructed to be movable and, in this connection, are referred to as holding-down sinkers.
With these holding-down sinkers, it is possible to keep the loose stitches pressed down and also to keep them out of the region of stitch formation of the succeeding stitches or out of the region of needle movement. Thereby, the conventional holding-down sinkers have both the task of serving as comb sinkers, i.e. of providing the coulier edges for the stitch formation as well as holding the old stitches down and preventing expansion into the stitch forming region. On the basis of their function as coulier edges, they must therefore also be provided and put into operation, i.e. be controlled, even when a holding-down is not required, for example when simple fabrics not having additional loose stitches are being manufactured. Thus, an alternative operation, with and without holding-down sinkers, is not possible.
A further disadvantage of the conventional flat knitting machines having holding-down sinkers is that with two bedded holding-down sinkers, such types of holding-down sinkers together with the appertaining control devices are required on both beds. In their forward position, the holding-down sinkers thereby come more or less closely together and thus effect the holding-down of the stitches. The construction and manufacturing cost of these conventional flat knitting machines is high because for each bed, sinkers, sinker beds and corresponding control devices in the cams are required. Moreover, the control of the sinker movement has to be very exact due to the oppositely located holding-down sinkers which, once more, reduces the operational reliability or increases the cost for providing small tolerances.